Phasers that use hydraulic oil pressure to control the phase of the cams on engine camshafts are known, an example being described in U.S. Pat. No. 6,725,817. The phaser in the latter patent specification, in common with those to be described herein, is a twin-vane phaser having two output members, the phase of each of which is adjustable relative to a stator driven by the engine crankshaft. The invention is not however restricted to twin-vane phasers and is also applicable to single vane phasers in which the phase of only one output member is adjustable relative to the engine crankshaft.
In order to supply hydraulic oil under pressure to the working chambers of such a hydraulic phaser, it is known, for example from U.S. Pat. No. 6,247,436, that an engine mounted front cover or oil feed manifold can convey oil from an oil pump via a control valve to the phaser.
As all hydraulic camshaft phasers require two or more oil lines (supply and return), one needs to provide a rotary hydraulic coupling to establish a connection between the lines in the cover/manifold and the phaser.
A known oil feed arrangement is described in EP 1473443 where the camshaft has an axially projecting extension that is rotatably and sealingly received in an opening formed in the front cover/manifold to enable the oil passage in the camshaft to communicate with the oil galleries in the engine cover. Such an extension is hereinafter referred to as a “cam nose”.
Although the invention could be equally applicable to a spigot style of oil feed, as described in U.S. Pat. No. 6,725,817, it will be described herein with reference to an oil feed arrangement with a cam nose similar to that of EP 1473443.
FIG. 1 of the accompanying drawings shows a sectional view through a camshaft phaser 10 fitted over a protruding cam nose 12 of an assembled SCP (single cam phaser) camshaft 14 having cams 16 and 18 that can be rotated relative to one another. Some cams, such as the cam 16, are fixed to and rotate with an outer tube 20 of the SCP camshaft 14 while other cams, such as the cams 18, rotate with the inner shaft 22 of the SCP camshaft 14 to which they are coupled by means of a pin 24 passing through a circumferentially elongated slot in the outer tube 20. A bearing 26 fixed to the outer tube 20 is connected by one or more pins 28 to be driven by the rear end plate 30 of the phaser 10, while the inner shaft 22 is driven by a front end plate 32 of the phaser 10 to which it is coupled by a nut 34.
The phaser 10 is a known twin-vane cam phaser (see for example U.S. Pat. No. 6,725,817) of which the internal construction is not shown in FIG. 1. A stator 38 solid with an engine driven sprocket 36 is formed with arcuate recesses that receive vanes secured to the end plates 30 and 32. The vanes divide each recess into different working chambers and by controlling the oil supply to and from the different working chambers, the end plates 30 and 32 of the phaser, acting as output members, can be rotated relative to the stator 38.
The known cam noses, as depicted in FIG. 1, are simple turned parts with axial drillings 40 that form part of the phaser oil feeds or returns. The cam nose 12 of FIG. 1 is shown in more detail in the perspective, side, end and sectional views of FIGS. 2a to 2d has four such axial drillings, one pair of supply and return passages for controlling each of the two output members.
Packaging limitations dictate that the outer diameter of the cam nose 12 (within which the axial drillings 40 must be packaged) must be small. This makes it costly and difficult to machine the axial drillings in the cam nose, resulting in a design that is unattractive for volume production. Furthermore, it is hard to utilise the potential flow area within the cam nose as the drillings cannot be packaged together very closely. A further shortcoming is that the central portion, generated in-between the drillings 40, is of no use as it offers minimal structural benefit.